1. What make
2.What model
3 what engine size
4 what fuel type.
5. Is it a motorhome
Timing, clutch, or knackered compression. get compression tested.
TEST RUN
All reves and no go up hill but ok down hill i had a car like that and knew from that it was the clutch slipping and needed replacing. try test on flat and clear road change through gears to top gear put foot down quick if it revs and is slow or no go in take off it seems to me its a new clutch job. if it performs resonable it could be any other fault like timming,valves or compression. As i'm not mechanic and going by symptoms experience copy and paste your question in to the VANS section.
If general purpose van why place it in motorhome and caravan section. should be in vans section.
bob
June 2011